China
Africa
Explore chapters and articles related to this topic
Analysis of Pesticide Residues by Chromatographic Techniques Coupled with Mass Spectrometry
Published in José L. Tadeo, Analysis of Pesticides in Food and Environmental Samples, 2019
Wan Jing, Jin Maojun, Jae-Han Shim, A.M. Abd El-Aty
Electrospray ionization (ESI) source is an ionization mode mainly used in liquid chromatography–mass spectrometry. It serves as both an interface between the liquid chromatograph and the mass spectrometer and as an ionization device. Its main component is an electrospray nozzle consisting of a two-layer casing. The inner layer of the nozzle is the liquid chromatography effluent, while the outer layer is the atomization gas, which is usually nitrogen gas with a large flow. The liquid sample is dispersed into droplets with the aid of the atomization gas. In addition, there is an auxiliary gas nozzle at the oblique front of the nozzle. The role of the auxiliary gas is to quickly evaporate the solvent of the droplet. The charge density on the surface of droplets gradually increases during evaporation, and when it reaches a critical value, ions can evaporate from the surface. Ions pass through the sampling hole and enter the analyzer by means of the voltage between the nozzle and the cone hole. The voltage applied to the nozzle can be positive or negative. By adjusting the polarity, a positive or negative ion mass spectrum can be obtained.
Capillary Electrophoresis
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
The MS detector is commercially available and is a powerful detector used in CE due to its sensitivity, universality, and ability to obtain structural information. To obtain the identity of sample components, capillary electrophoresis can be directly coupled with mass spectrometers. In most systems, the capillary outlet is introduced into an ion source that uses electrospray ionization (ESI). The resulting ions are then analyzed by the mass spectrometer. MS detector limits of detection are typically 10−8–10−9 M [27]. The mass spectrometer requires volatile buffer solutions, which will affect the range of separation modes that can be employed and the degree of resolution that can be achieved. Interfaces requiring the use of a sheath flow are the coaxial sheath-flow interface or the liquid-junction interface. Sheathless interfaces include the low flow electrospray or nanospray device [129]. The disadvantages of the MS detector are cost and interferences in the analysis. CE-MS requires the direct coupling of the ionization method to a liquid-phase separation technique to permit MS detection. There are challenges in achieving stability, reproducibility, and sensitivity of CE-MS for routine use. However, improvements have been made in the reliability and reproducibility of the interface. Applications of CE-MS have been applied for the analysis of peptides [130], drug analysis [131], food analysis [132], proteomics [133], and small chiral and achiral compounds [134].
Proteins and proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
MS is an analytical technique for the determination of the elemental composition of a sample or molecule. It allows rapid and high-through-put identification of proteins and sequencing of peptides most often after in-gel digestion. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios. MS instruments consist of three modules: an ion source, which can convert gas phase sample molecules into ions (or, in the case of electrospray ionization (ESI), move ions that exist in solution into the gas phase); a mass analyzer, which sorts the ions by their masses by applying electromagnetic fields; and a detector, which measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present. The technique has both qualitative and quantitative uses. These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. MS is now in common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds. MS is an important emerging method for the characterization of proteins. The two primary methods for ionization of whole proteins are ESI and matrix-assisted laser desorption/ionization. In keeping with the performance and mass range of available mass spectrometers, two approaches are used for characterizing proteins. In the first, intact proteins are ionized by either of the two techniques described earlier, and then introduced to a mass analyzer. This approach is referred to as “top-down” strategy of protein analysis. In the second, proteins are enzymatically digested into smaller peptides using proteases such as trypsin or pepsin, either in solution or in gel after electrophoretic separation. Other proteolytic agents are also used. The collection of peptide products are then introduced to the mass analyzer. When the characteristic pattern of peptides is used for the identification of the protein, the method is called peptide mass fingerprinting. If the identification is performed using the sequence data determined in tandem with MS analysis, it is called de novo sequencing. These procedures of protein analysis are also referred to as the “bottom-up” approach.
The application of structural analysis in the investigation of solvent extraction mechanism
Published in Journal of Coordination Chemistry, 2022
Shan Zhu, Huiping Hu, Song Li, Chengyong Wang
Electrospray ionization mass spectrometry (ESI-MS) is a fast, sensitive, and continuous method for determination of liquid samples. The time range (milliseconds) employed in the detection is short enough to prevent equilibrium transformation of the extracted species in the ionization process, and is suitable for polar, volatile and thermally unstable compounds, especially with weak interaction [28]. The advantages of this method were to determine the stoichiometry of extracted complexes in solution phase and the stability of extracted complexes in the gas phase. Despite the advantages of ESI-MS, investigation on the structure of extracted complexes in solvent extraction process are few [29–33]. Skarnemark [28] investigated the extraction mechanism of the extraction of actinides and lanthanides from nitrate solution by ESI-MS. The results indicated that the extracted complexes contain three nitrate ions, one of which is directly coordinated with metal ions, while the other two nitrate ions are located in the second coordination layer with weak interaction.
β-Agonist in the environmental waters: a review on threats and determination methods
Published in Green Chemistry Letters and Reviews, 2022
Usman Armaya’u, Marinah Mohd Ariffin, Saw Hong Loh, Wan Mohd Afiq Wan Mohd Khalik, Hanis Mohd Yusoff
The electrospray ionization (ESI) is a gentle ionization source in which very little residual energy is kept by the analyte, and typically no fragmentation occurs during the ionization process. Furthermore, extremely weak noncovalent interactions were maintained in the gas phase during the ionization process (94). ESI was used as an ion source when using the LC-MS/MS systems because it enables quick, precise, and responsive analysis, as a source of low-energy ionization ESI typically does not induce molecular ion fragmentation and is suggested for thermally labile and polar compounds, especially, β-agonists compounds (95). Salbutamol was detected in the river and waste effluents by Al-Odaini in the year 2010 (95), SPE-LC-ESI-MS/MS was used to obtain good recoveries above 70% in all the target analytes in both the matrices. The LOD of the method was 0.2–281 ng/L and the detection limit for the analyte in both matrices was greater than the method detection limit of 3 ng/L. SPE-LC-ESI-MS/MS method for the positive detections and quantification of salbutamol in wastewaters sampled from 7 Canadian STPs was developed by Lee(6). The developed method was able to detect terbutaline at a limit range of 6-11 ng/L with the recovery on the compounds better than 85%. A minor modification of Lee’s method (6), was successfully applied by Salem (74), in a simultaneous determination of terbutaline in distilled and wastewaters. The optimized and validated method obtained an average recovery between 77.20-97.30% with method detection limits around 0.11–6.74 pg/mL and quantification limits of 0.14–22.88 pg/mL.